Portable devices, and in particular electronic equipment, such as mobile phones or small hand-held computers, any mobile and wireless devices include secondary power cells for power supply which are usually provided in the form of rechargeable power cells (rechargeable batteries) saving the user the costs and the inconvenience of regularly having to purchase new (not rechargeable) cells. Rechargeable cells are preferred due to economical and environmental reasons.
A charging operation of the rechargeable cells can be performed by using an adaptor or charger which takes power from a public electrical power network (mains power supply) or other adequate sources of power. The adaptor or charger connected to the mains power supply is further connected by a supply line and a suitable connector to the portable device, and charging starts immediately upon physically connecting the devices. When the charging operation is completed, this is usually displayed on the display means of the portable device, and charging may be stopped or reduced.
Conventional adaptors or chargers exhibit a number of problems when used for recharging secondary cells of any arbitrary portable device.
The adaptors and chargers usually require the users to plug a connector into the device, and the devices should better not be used in wet environment due to the possibility of corroding or shorting out the contacts, and also such devices cannot be used in flammable gaseous environment due to the possibility of creating electrical sparks.
The problems above can be solved by replacing the conventional chargers or adaptors by inductive chargers for transmitting the electric energy for charging the batteries of a device by means of an electromagnetic field and a direct magnetic coupling without a physical electrical connection, i.e. without using plug and socket. Since the inductive chargers for wireless charging remove the need to have open electrical contacts in conjunction with a cable connection it is possible to use such chargers in wet or dusty environments since both the chargers and the device to be charged can be provided as sealed devices without physical contacts being exposed to the outside. The basical principle of such inductive chargers involves magnetic cores with a coil wound around the cores, and a generated magnetic field penetrating through the air gap or a region of non-magnetic material between the devices and forming a magnetic inductive link for power transmission.
The arrangements as mentioned above, however, lead to a non-uniform flux distribution of the magnetic field so that the charging effectivity is largely dependent from the correct placement of the portable device on the inductive charger.
According to further developments there is provided a planar inductive battery charger, an example of which is disclosed in prior art document WO 03/105308 A1. On a charging surface of a planar charging module is at least one planar coil or a plurality of planar coils arranged to generate a planar magnetic field. By means of this planar magnetic field an inductive coupling to a device placed thereon is established when this device (a portable device such as a mobile phone) is also equipped with a corresponding magnetic coil. The battery included in the portable device can be charged when the portable device is placed on the planar surface of the charging module and the magnetic field of the charging module is coupled to the coil of the portable device. That is, when the portable device is placed on the charging module which constitutes a docking station with integrated inductive link for power transfer, this also poses several other problems.
For almost every portable device there is the need of having a different docking station, since the shape of the devices may vary considerably from device to device and manufacturer to manufacturer, and the users need to have several different docking stations for different devices in use. Moreover, every docking station or every charging module needs to be plugged into sockets of a mains power supply, and when several docking stations are used together, they take up space in plug strips and create a messy and confusing tangle of wires.
In many cases portable or mobile devices to be charged must be placed into a stand, usually one device per one docking station, causing inconvenience for the user. In other cases the device position or the orientation thereof is pre-defined for proper and optimized charging. This sets limitations for the user interface of the device (position on the desk, horizontal and axial viewing angle to the display means of the device).
To overcome such limitations of inductive power transfer systems, which require that secondary devices need to be placed on predefined positions on the charging module thereof, power transfer pads have been developed, these pads generating an electromagnetic field over a large area, and preferably the whole pad area. The user can simply place one or more devices the batteries of which are to be charged on the pad with no requirement to place them accurately or at a predetermined position.
In the above-described planar charging module of document WO 03/105308 A1 an array of planar coils is provided and only coils which are needed are activated. The electromagnetic field generated is close to the pad and only around the position where the portable device is placed. The relative location of the portable device on the planar charging module can be sensed and a control unit can then activate the appropriate coils to deliver power to these coils which in turn deliver power via the magnetic field to the portable device.
Specifically, when the portable device is used in an extensive manner and the battery thereof is completely exhausted or when the battery is damaged and cannot provide any suitable power to power-up the portable device, it is necessary to charge the battery power source of the portable device in an appropriate manner. It may also occur that the battery is not correctly mounted to the portable device and cannot power the portable device. When the portable device suffers from such a “dead battery condition” or a corresponding malfunction it is difficult to charge the battery power source of such a portable device as the correct or optimized charging power cannot be determined when the portable device suffering from the dead battery condition is placed on the charging module (charging pad) of a power transfer device.